A computer network is composed of a set of nodes and a set of links that connect one node to another. For instance, a computer network may be composed of a set of routers while the set of links may be cables between the routers. When a first node in the network sends a message to a second node in the network, the message may pass through many links and many nodes. The links and nodes the message passes through while traveling from the first node to the second node is referred to as a path. For example, suppose the message passes through a third node while traveling from the first node to the second node. In this case, the path leads from the first node to the third node to the second node.
Packet-based computer networks increasingly utilize label switching protocols for traffic engineering and other purposes. In a label switching network, label switching routers (LSRs) use Multi-Protocol Label Switching (MPLS) signaling protocols to establish label switched paths (LSPs). The LSRs utilize MPLS protocols to receive MPLS label mappings from downstream LSRs and to advertise MPLS label mappings to upstream LSRs. When an LSR receives an MPLS packet from an upstream router, it switches the MPLS label according to the information in its forwarding table and forwards the packet to the appropriate downstream LSR.
Point-to-multipoint (P2MP) label switched paths (LSPs) are increasingly being used. For example, P2MP LSPs are often used to carry multicast traffic, such as Internet Protocol Television (IPTV), desktop conferences, corporate broadcasts, music and video web casts, and other forms of multimedia content. P2MP LSPs may be used with private network instances, such as, multicast virtual private local area network service (multicast VPLS) instances, multicast virtual private network (MVPN) instances, and Internet Protocol (IP) multicast instances.
Links and nodes in a computer network may fail without warning. Consequently, one of the LSPs that the first node was using to communicate with the second node may stop functioning. To ensure that the first node and the second node do not send messages on a LSP that is not functioning, the nodes may periodically verify the status of the path by sending a message through the path and receiving a response through the path.
One mechanism for verifying connectivity along an LSP, referred to as “LSP ping,” is described by RFC4379 Kompella, K. and G. Swallow, “Detecting Multi-Protocol Label Switched (MPLS) Data Plane Failures”, RFC 4379, February 2006, hereby incorporated herein by reference. In general, LSP ping utilizes a form of MPLS “echo requests” and “echo replies” for detecting MPLS data plane failures and for verifying the MPLS LSP data plane against the control plane. However, in some situations, verifying the connectivity along a P2MP LSPs using LSP ping may be difficult due to relatively significant control plane processing required for LSP ping messages.